This invention generally relates to an electronic circuit which forms an astable multivibrator. More specifically, the present invention relates to a multivibrator which operates on a relatively low amount of voltage, consumes a relatively low amount of power, and is therefore suitable for use in battery-powered applications.
Multivibrators represent electrical timing circuits which produce pulses having predetermined timing parameters associated therewith. These timing parameters are often controlled through resistance-capacitance elements coupled into the multivibrator circuit. Astable multivibrators, also called free-running multivibrators, represent electrical circuits where one or more multivibrators are configured to operate as an oscillator, or to produce a continuous stream of pulses.
An astable multivibrator may advantageously control power to electrical circuits which perform various electrical functions in a battery-powered system. When these electrical functions accomplish their tasks using less than 100% of the available time, the circuits which perform these electrical functions may be deenergized for that portion of the time in which they are not performing their tasks. For example, sensing, data logging or communication may occur only a small fraction of each second, minute or hour. Accordingly, the circuits which perform such electrical functions may be energized only on a low duty cycle schedule to conserve battery power.
In such battery-powered systems, power consumption of an astable multivibrator represents a critical parameter because the astable multivibrator may remain energized 100% of the time. Only when the astable multivibrator output becomes active, or produces a pulse, will the circuits that perform particular electrical functions become energized so that they may perform their respective functions.
Conventional multivibrator circuits are not well suited for such an application. Typical multivibrator circuits consume excessive amounts of current. This excessive current consumption directly relates to excessive power consumption. Additionally, such circuits typically require an excessive power supply voltage which forces the use of additional battery cells for energization of the multivibrator circuit. In addition, the excessive supply voltage also relates directly to excessive power consumption. Furthermore, such conventional circuits often consume excessive amounts of current during the longer duration portion of the energization duty cycle when power is not applied to the functional circuit. In other words, such circuits often consume more power than is necessary, while the multivibrator output is inactive.